Japanese Oak Wilt

**This organism is not known to be present in the United States but poses a threat. Japanese oak wilt is a disease caused by the fungus — Raffaelea quercivora. It was discovered in 2002 in association with dying oak trees in Japan. The oak ambrosia beetle, Platypus quercivorus, feeds on the Raffaelea quercivora fungus and carries it to new hosts. Typically, ambrosia beetles and their associated fungi do not kill healthy trees; however this is not the case with Japanese oak wilt. Scientists now attribute the death of more than 200,000 oak trees to this disease, annually since 1980.


USDA plant pathologists and other scientists have assessed the potential impacts that Japanese oak wilt could have on our commercial forest and natural ecosystems and have identified it as a serious threat. Risk assessments have also been conducted on the insect vector — Platypus quercivorus — because both the insect and the pathogen need to be present in order to cause disease.


Neither Raffaelea quercivora nor Platypus quercivorus are known to be in the United States. The likely pathway for introduction would be through infested wood materials.

Due to the cryptic nature of the beetle and the availability of host material around ports of entry, there will always be the chance that the oak ambrosia beetle could be introduced.


Hosts identified in Japan include a variety of oak species. The pathogen was isolated from Quercus mongolica and Q. serrata. Host studies in Japan confirmed that the pathogen can cause disease on several other species. It is important to note that it is not known what oaks would be susceptible to this disease here in the US.


Think you've spotted this pest?

If you think you've found this pest in your landscape contact your local extension office to see about sending in a sample.
Find your local extension office here.